Exemplary embodiments of the present invention relate generally to a terrestrial positioning and timing system (“TPTS” or “System”) that draws upon the heritage of current terrestrial distance, bearing, and positioning systems used in aviation, while incorporating new concepts for signal structure and implementation techniques to provide a terrestrial user position, navigation, and time (“PNT”) service. The TPTS also draws upon the concepts and techniques of terrestrial based differentially corrected pseudo satellites (“pseudolites”), using a modified code division multiple access (“CDMA”) Global Positioning Systems (“GPS”) signal format.
The TPTS may be considered an alternative PNT service, for use when the GPS is not available. While the GPS is a popular satellite-based positioning system, other satellite-based positioning systems exist. The more general term for satellite-based positioning system is a Global Navigation Satellite System (GNSS). Other satellite-based position such as the Russian GLObal NAvigation Satellite System (GLONASS), the European Galileo, Chinese Bei Dou are other. The TPTS may be considered as an alternative PNT service, for use when these GNSSs are not available. While GPS provides good position accuracy, continuity, availability, and integrity for some aviation applications, its reliability for certain aviation services have come into question due to potential unfavorable consequences if GPS is not available. Distance, bearing, positioning, and timing services are also available from the national airspace system (“NAS”). Currently, each of these services has deficiencies in providing position, velocity, time (“PVT”) services within the NAS relative to the levels provided by a GPS based solution.
Current Distance Measurement Equipment (DME) is based primarily on pulsed modulation and determines an estimate of range from a user to a station. One of the fundamental limitations of the DME is the pulsed format where timing, and hence range accuracy, is derived from broadcast pulse timing. The Very High Frequency (VOR) Omni-directional Range (VOR) system is based in the VHF frequency band, and despite its name, provided bearing only to a station. The VOR system requires substantial ground facilities to minimize signal error and can have siting complications to minimize multipath. The Tactical Air Navigation (TACAN) combines aspects of the DME and VOR for a ground station that is capable of producing range and bearing from a station; however, its accuracy and limitations of accuracy are a function of the limitations and accuracies of the DME and VOR systems the TACAN uses as a basis. The Joint Tactical Information Distribution System (JTIDS) implements a complex signal format that is utilized by authorized (i.e., military) users. The Long Range Navigation (Loran) Systems has been recently decommissioned for operational use by the United States Government. Operational use of Loran (e.g., Loran-C or enhanced Loran) in other parts of the Globe have limited coverage area and require specialized equipment. Experience with global navigation satellite systems such as GPS, Glonass, and Galileo show that a code-division multiple access (“CDMA”) technique may provide excellent range accuracy performance because the signal bandwidth may be used for correlation of a spreading code and then integrated over time to produce good range estimation.
The need for position, velocity, or time of a mobile user is not limited to aviation applications. Just as aviation user could use the TPTS station in times when a supporting GNSS is not available, other types of users (e.g., land) can use a suitably configured TPTS station to support its position, velocity, or timing requirement.